An alliance of cancer charities has written to Iain Duncan Smith over their concerns patients will be pushed into poverty. Photograph: Stephen Hird/Reuters

An alliance of 30 cancer charities has written to Iain Duncan Smith to warn that thousands of people with cancer will be pushed into poverty. I share their worries.

In late January I was diagnosed with stomach cancer. The prognosis was grim: it emerged the cancer had spread to my liver and oesophagus, and I was given six to nine months to live – maybe 12 if I responded well to chemotherapy. The last thing my partner and I were thinking about was my financial situation.

My oncologist referred me to a Sheffield-based cancer support charity that took me through the disability living allowance (DLA) form. I was shocked to discover that the entitlement was not backdated to the date of diagnosis – which is the date I was unable to continue work – but rather the date of application. For me it was two weeks' worth (a 12th of my future life expectancy) and I had been fast-tracked. What about others who are not so lucky? They could have to wait months. My case is atypical: 26-year-old men don't generally get stomach cancer. People in my position are usually much older, with kids to support and a mortgage to pay back. How on earth do they cope with the loss of earnings?

I wrote to Duncan Smith and asked him to change the rule, as it's within his power to do so. He didn't deem my enquiry worthy of a response, and as a result I've decided to exploit my position in order to shame those in power to do the reasonable and compassionate thing.

I have never before claimed benefits, so I had no experience with the benefits system. My first impressions were not good: I saw a system stacked against the most vulnerable. In this maze, if I wanted to complain about the current situation to the Department for Work and Pensions, I would have to phone a premium-rate number. And if I wished to contest a decision they made, legal aid was no longer available to me because of the £350m cuts announced by the justice secretary last November.

Benefit claimants, as well as people receiving DLA, are being mercilessly attacked in the latest round of spending cuts. For example, the funding of the cancer charity that provided me with vital support is being slashed. Yet we have a huge problem with tax avoidance in this country. According to the government's most recent figures, £42bn pounds was lost through the most wealthy corporations and individuals not paying their taxes – although some believe it to be a staggering £120bn. Sticking to the government's own figures, projected over the four years of spending cuts, that's £168bn compared with £83bn worth of cuts to services for the most vulnerable.

The government is very fond of comparing the economy to a family budget. It seems perverse to me to expect a family to cut down on their food bills when there's a lodger in the house not paying their way. Indeed, at this most difficult of times, the government even found the resources to cut corporation tax by 4%. If only the people in real difficulties were given similar breaks.

For too long, both the major political parties have pandered to lazy, middle-England stereotypes of the dreaded "benefit scroungers" in order to win easy seats in swing constituencies. I hope I can have a small influence in making people reassess those preconceptions. My remaining time will be spent attempting to shame those in power into doing the right thing. I hope you will help me in this endeavour.